In recent years, there has been an increasing interest in the use of ceramics for structural applications historically served by metals. The impetus for this interest has been the superiority of ceramics with respect to certain properties, such as corrosion resistance, hardness, modulus of elasticity, and refractory capabilities, when compared with metals.
Current efforts at producing higher strength, more reliable, and tougher ceramic articles are largely focused upon (1) the development of improved processing methods for monolithic ceramics and (2) the development of new material compositions, notably ceramic matrix composites. A composite structure is one which comprises two or more different materials which are intimately combined in order to attain desired properties of the composite. For example, two different materials may be intimately combined by embedding one in a matrix of the other. A ceramic matrix composite structure typically comprises a ceramic matrix which incorporates one or more diverse types of filler materials such as particulates, fibers, rods, and the like.
There are several known limitations or difficulties in substituting ceramics for metals, such as scaling versatility, capability to produce complex shapes, satisfying the properties required for the end use application, and costs. Several copending patent applications, and Issued Patents, assigned to the same owner as this application (hereinafter sometimes referred to as "Commonly Owned Patent Applications and Patents"), overcome these limitations or difficulties and provide novel methods for reliably producing ceramic materials, including composites. The method is disclosed generically in Commonly Owned U.S. Pat. No. 4,713,360, issued on Dec. 15, 1987, in the names of Marc S. Newkirk et al and entitled "Novel Ceramic Materials and Methods for Making Same". This Patent discloses a method of producing self-supporting ceramic bodies grown as the oxidation reaction product of a molten parent precursor metal which is reacted with a vapor-phase oxidant to form an oxidation reaction product. Molten metal migrates through the formed oxidation reaction product to react with the oxidant thereby continuously developing a ceramic polycrystalline body which can, if desired, include an interconnected metallic component. The process may be enhanced by the use of one or more dopants alloyed with the parent metal. For example, in the case of oxidizing aluminum in air, it is desirable to alloy magnesium and silicon with the aluminum to produce alpha-alumina ceramic structures. This method was improved upon by the application of dopant materials to the surface of the parent metal, as described in Commonly Owned U.S. Pat. No. 4,853,352, which issued on Aug. 1, 1989, from U.S. patent application Ser. No. 220,935, filed Jun. 23, 1988, which was a continuation-in-part of U.S. application Ser. No. 822,999, filed Jan. 27, 1986 (and now abandoned), which was a continuation-in-part of U.S. application Ser. No. 776,965, filed Sep. 17, 1985 (and now abandoned), which was a continuation-in-part of U.S. application Ser. No. 747,788, filed Jun. 25, 1985 (and now abandoned), which was a continuation-in-part of U.S. application Ser. No. 632,636, filed Jul. 20, 1984 (and now abandoned), all in the names of Marc S. Newkirk et al and entitled "Methods of Making Self-Supporting Ceramic Materials". Above-mentioned U.S. application Ser. No. 747,788, corresponds to European Patent Application No. 85305107.6, which was published on Jan. 22, 1986, as European Patent Application Publication No. 0169067.
A similar oxidation phenomenon was utilized to grow oxidation reaction product into a filler material to produce ceramic composite bodies, as described in Commonly Owned U.S. patent application Ser. No. 265,835, filed Nov. 1, 1988, now U.S. Pat. No. 4,916,113, which issued on Apr. 10, 1990, and which was a continuation of U.S. application Ser. No. 819,397, now U.S. Pat. No. 4,851,375, which issued on Jul. 25, 1989, and was a continuation-in-part of U.S. application Ser. No. 697,876, filed Feb. 4, 1985 (and now abandoned). All of the patent applications and patents mentioned in this paragraph were filed in the names of Marc S. Newkirk et al. and were entitled "Composite Ceramic Articles and Methods of Making Same". However, U.S. Pat. No. 4,851,375, issued with the title "Methods of Making Composite Ceramic Articles Having Embedded Filler", and U.S. Pat. No. 4,916,113, issued with the title "Methods of Making Composite Ceramic Articles". Above-mentioned U.S. application Ser. No. 819,397, corresponds to European Patent Application No. 86300739.9, which was published on Sep. 3, 1986, as European Patent Application Publication No. 0193292. The patent applications and patents, described immediately above, disclose novel methods for producing a self-supporting ceramic composite by growing an oxidation reaction product from a parent metal into a permeable mass of filler, (e.g., a silicon carbide particulate filler) thereby infiltrating the filler with a ceramic matrix. The resulting composite, however, has no defined or predetermined geometry, shape, or configuration.
A method for producing ceramic composite bodies having a predetermined geometry or shape is disclosed in Commonly Owned and Copending U.S. patent application Ser. No. 338,471, filed Apr. 14, 1989, which is a continuation of U.S. application Ser. No. 861,025, filed May 8, 1986 (and now abandoned), both in the names of Marc S. Newkirk et al. In accordance with the method in this U.S. Patent Application, the developing oxidation reaction product infiltrates a permeable preform of filler material (e.g., a silicon carbide preform material) in a direction towards a defined surface boundary. Above-mentioned U.S. application Ser. No. 861,025, corresponds to European Patent Application No. 87630075.7, which was published on Nov. 11, 1987, as European Patent Application Publication No. 0245192.
It was discovered that high shape fidelity is more readily achieved by providing the preform with a barrier means, as disclosed in Commonly Owned U.S. patent application Ser. No. 295,488, filed Jan. 10, 1989, which is a continuation of U.S. patent application Ser. No. 861,024, filed May 8, 1986, now U.S. Pat. No. 4,923,832, which issued on May 8, 1990, all in the names of Marc S. Newkirk et al. This method produces shaped self-supporting ceramic bodies, including shaped ceramic composites, by growing the oxidation reaction product of a parent metal to a barrier means spaced from the metal for establishing a boundary or surface. Above-mentioned U.S. application Ser. No. 861,024, corresponds to European Patent Application No. 87630076.5, which was published on Nov. 11, 1987, as European Patent Application Publication No. 0245193.
Ceramic composite bodies having a cavity with an interior geometry inversely replicating the shape of a positive mold or pattern are disclosed in Commonly Owned U.S. patent application Ser. No. 329,794, filed Mar. 28, 1989, which is a divisional of U.S. patent application Ser. No. 823,542, filed Jan. 27, 1986, now U.S. Pat. No. 4,828,785, which issued May 9, 1989, all in the names of Marc S. Newkirk, et al, and in Commonly Owned U.S. Pat. No. 4,859,640, which issued on Aug. 22, 1989, from U.S. patent application Ser. No. 896,157, filed Aug. 13, 1986, in the name of Marc S. Newkirk. Above-mentioned U.S. Application Serial No. 823,542, corresponds to European Patent Application No. 87300409.7, which was published on Sep. 2, 1987, as European Patent Application Publication No. 0234704. Above-mentioned U.S. application Ser. No. 896,157, corresponds to European Patent Application No. 87630109.4, which was published on Mar. 9, 1988, as European Patent Application Publication No. 0259239.
A technique whereby additional molten parent metal is supplied from a reservoir to the initial body of molten metal is disclosed in Copending and Commonly Owned U.S. patent application Ser. No. 478,845, filed Feb. 12, 1990, as a continuation of U.S. patent application Ser. No. 168,358, filed Mar. 15, 1988, now U.S. Pat. No. 4,918,034, which issued on Apr. 17, 1990, and which was a continuation-in-part of U.S. patent application Ser. No. 908,067, filed Sep. 16, 1986, now U.S. Pat. No. 4,900,699, which issued on Feb. 13, 1990. All of the patent applications and patents described in this paragraph were entitled "Reservoir Feed Method of Making Ceramic Composite Structures and Structures Made Thereby". U.S. patent applications Ser. Nos. 478,845 and 168,358, were both filed in the names of Weinstein et al. U.S. patent application Ser. No. 908,067, was filed in the names of Newkirk et al. Above-mentioned U.S. application Ser. No. 908,067, corresponds to European Patent Application No. 87630176.3, which was published on Mar. 30, 1988, as European Patent Application Publication No. 0262075. The reservoir feed method, discussed above, has been successfully applied to form ceramic matrix or ceramic matrix composite structures. According to the method of this invention, the ceramic matrix or ceramic matrix composite body which is produced comprises a self-supporting ceramic matrix composite structure which includes a ceramic matrix obtained by the oxidation reaction of a parent metal with an oxidant to form a polycrystalline material. In the embodiment of the process whereby a ceramic matrix composite body is produced, a body of the parent metal and a permeable mass or preform of filler material are oriented relative to each other so that formation of the oxidation reaction product will occur in a direction toward and into the filler material. The parent metal is described as being present as a first source and as a reservoir, the reservoir of metal communicating with the first source due to, for example, gravity flow. The first source of molten parent metal reacts with the oxidant to begin the formation of the oxidation reaction product. As the first source of molten parent metal is consumed, it is replenished, preferably by a continuous means, from the reservoir of parent metal. This replenishment of the first source of parent metal continues as the growth of oxidation reaction product infiltrates the filler material. Thus, the reservoir assures that ample parent metal will be available to continue the process until the oxidation reaction product has grown to a desired extent.
A method for tailoring the constituency of the metallic component of a ceramic matrix composite structure is disclosed in Copending and Commonly Owned U.S. patent application Ser. No. 269,152, filed Nov. 9, 1988, in the names of Robert C. Kantner et al. and entitled "Method for in situ Tailoring the Metallic Component of Ceramic Articles and Articles Made Thereby", which is a continuation of Commonly Owned U.S. patent application Ser. No. 152,518 filed on Feb. 5, 1988, in the same names and having the same title; which was a continuation-in-part of U.S. patent application Ser. No. 908,454 (now abandoned), filed Sep. 17, 1986, in the names of Marc S. Newkirk et al. and having the same title. U.S. patent application Ser. No. 152,518, issued on Apr. 4, 1989, as U.S. Pat. No. 4,818,734, and was entitled "Method For In Situ Tailoring The Metallic Component of Ceramic Articles". Finally, U.S. patent application Ser. No. 389,506, was filed on Aug. 2, 1989, in the names of Marc S. Newkirk et al., as a continuation of U.S. application Ser. No. 908,454, and was entitled "Method for In Situ Tailoring the Metallic Component of Ceramic Articles and Articles Made Thereby". Above-mentioned U.S. application Ser. No. 908,454, corresponds to European Patent Application No. 87630161.5, which was published on Apr. 6, 1988, as European Patent Application Publication No. 0263051. Each of these applications and Patent discloses a method for tailoring the constituency of the metallic component (both isolated and interconnected) of ceramic matrix and ceramic matrix composite bodies during formation thereof to impart one or more desirable characteristics to the resulting body. Thus, desired performance characteristics for the final ceramic matrix or ceramic matrix composite body are advantageously achieved by incorporating the desired metallic component in situ, rather than from an extrinsic source, or by post-forming techniques.
As discussed in these Commonly Owned Patent Applications and Patents, novel polycrystalline ceramic matrix materials or polycrystalline ceramic matrix composite materials are produced by the oxidation reaction between a parent metal and an oxidant which may be a solid, liquid and/or a gas. In accordance with the generic process disclosed in these Commonly Owned Patent Applications and Patents, a parent metal (e.g., aluminum) is heated to an elevated temperature above its melting point but below the melting point of the oxidation reaction product to form a body of molten parent metal which reacts upon contact with an oxidant to form the oxidation reaction product. At this temperature, the oxidation reaction product, or at least a portion thereof, is in contact with and extends between the body of molten parent metal and the oxidant, and molten metal is drawn or transported through the formed oxidation reaction product and towards the oxidant. The transported molten metal forms additional fresh oxidation reaction product upon contact with the oxidant, at the surface of the previously formed oxidation reaction product. As the process continues, additional metal is transported through this formation of polycrystalline oxidation reaction product thereby continually "growing" a ceramic structure of interconnected crystallites. The resulting ceramic matrix body may contain metallic constituents, such as non-oxidized constituents of the parent metal, and/or voids. Oxidation is used in its broad sense in all of the Commonly Owned Patent Applications and Patents discussed in this application, and refers to the loss, or sharing, of electrons by a metal to, or with, an oxidant which may be one or more elements and/or compounds. Accordingly, elements other than oxygen may serve as an oxidant.
In certain cases, the parent metal may require the presence of one or more dopants in order to influence favorably or to facilitate growth of the oxidation reaction product. Such dopants may at least partially alloy with the parent metal at some point during or prior to growth of the oxidation reaction product. For example, in the case of aluminum as the parent metal and air as the oxidant, dopants such as magnesium and silicon, to name but two of a larger class of dopant materials, can be alloyed with aluminum, and the created growth alloy is utilized as the parent metal. The resulting oxidation reaction product of such a growth alloy comprises alumina, typically alpha-alumina.
Novel ceramic matrix composite structures and methods of making the same are also disclosed and claimed in certain of the aforesaid Commonly Owned Patent Applications and Patents which utilize the oxidation reaction to produce ceramic matrix composite structures comprising a substantially inert filler (note: in some cases it may be desirable to use a reactive filler, e.g., a filler which is at least partially reactive with the advancing oxidation reaction product and/or parent metal) which is infiltrated by and embedded in the polycrystalline ceramic matrix. As a first step, a parent metal is positioned adjacent to a permeable mass of filler material which can be shaped and/or treated to be a self-supporting preform. The parent metal is then heated to form a body of molten parent metal which is reacted with an oxidant, as described above, to form an oxidation reaction product. As the oxidation reaction product grows and infiltrates the adjacent mass of filler material, molten parent metal is drawn through the previously formed oxidation reaction product within the mass of filler material and reacts with the oxidant to form additional fresh oxidation reaction product at the surface of the previously formed oxidation reaction product, as described above. The resulting growth of oxidation reaction product infiltrates or embeds the filler material and results in the formation of a ceramic matrix composite structure comprising a polycrystalline ceramic matrix embedding the filler material. As also discussed above, the mass of filler material (or preform) may utilize a barrier means to establish a boundary or surface for the ceramic matrix composite structure.
Thus, the aforesaid Commonly Owned Patent Applications and Patents describe the production of ceramic matrix and ceramic matrix composite bodies comprising oxidation reaction products which are readily grown to desired sizes and thicknesses heretofore believed to be difficult, if not impossible, to achieve with conventional ceramic processing techniques.
The entire disclosures of all of the foregoing Commonly Owned Patent Applications and Patents are expressly incorporated herein by reference.